This invention is directed to multicomponent hot melt compositions which form pressure-sensitive adhesives upon cure at reduced energy requirements.
U.S. Pat. No. 3,973,788 to Pekko assigned to the common assignee of this invention and incorporated herein by reference, describes a label construction where the underside of a clear polyester facestock is printed with intelligent indicia which printing is subsequently coated with a pressure-sensitive adhesive. There is then added a release liner. In the construction, printing is protected from abrasion or chemical attack by the facestock. An application of such labels is the automotive industry where the label is applied to surfaces in the engine compartment. Commonly, the adhesive is pigmented to conform to or contrast the color of the substrate and/or enhance printing visibility.
The process for producing such labels is complex and expensive. First, the back side of the facestock is printed, then the adhesive is applied to the label from transfer tape constructions of highly pigmented solution adhesives. To date, only solution acrylic adhesives have proven commercially feasible for this application. After transfer lamination, the labels are die cut and the matrix stripped off.
More recently, a process has been developed where printing and adhesive coating may be accomplished in tandem. In this process it is possible to UV cure the adhesive. The process is much simpler, less time consuming, and eliminates the need for the additional release liner attendant to the use of transfer adhesives. To be useful in the process, the adhesives must be hot melt adhesives of low melt viscosity. For automotive applications, the adhesive must display high temperature motor oil resistance which, due to melt viscosity restrictions, must be achieved by cross-linking.
The present invention is therefore directed to curable low viscosity pressure-sensitive adhesive formulations which are adaptive to application by hot melt processes which include printing and upon cure form pressure-sensitive adhesives useful for automotive applications especially where oil resistance is required.